Several diseases cause destruction of joints, resulting in chronic pain and impaired flexibility and agility. The problem is most pronounced in patients who suffer from chronic rheumatoid arthritis, but is also pronounced in, for instance, osteoarthritis (wear of cartilage) and in articular cartilage injuries after fractures and bacterial infections. In many of these cases the diseased and injured joint is replaced by an artificial joint structure.
However, experience has shown that too great an ambition to completely imitate the function of a normal joint in many cases results in failure. The artificial joint will easily be too complicated. For a rheumatic who has no joint function at all in, for instance, in hands, it is not necessary to aim at regaining a fully normal joint function via prosthetic operation. The aim should instead be to obtain a painless joint with a stability and a certain amount of movability, which makes the hand usable. Thus, the aim of the joint structure must always be related to the patient's needs.
The main difficulties when constructing artificial joints in e.g. the hand have been (1) to provide an artificial joint with satisfactory properties and (2) to fix the artificial joint to adjoining bones in a satisfactory manner.
WO 97/26846 discloses a prosthetic device comprising a joint body which includes one or more substantially helical spring means arranged between two fixing elements which are adapted to be connected to adjoining bone parts. This prosthetic device obviates many of the drawbacks that are associated with other known artificial prosthetic devices for joints that are available today. However the springs of this system is always susceptible to wear and friction, especially when forces are applied. Also the endurance of the springs is essential for the function of the prosthetic device.